The present disclosure generally relates to an apparatus for preparing gypsum products from starting materials including calcined gypsum and water, and more particularly relates to an improved gypsum slurry mixer gate for use in conjunction with a slurry mixer of the type employed in supplying agitated gypsum slurry to a wallboard production line.
It is well known to produce gypsum products by dispersing calcined gypsum in water to form a slurry, and then casting the slurry into a desired shaped mold or onto a surface and allowing the slurry to set to form hardened gypsum by reaction of the calcined gypsum (calcium sulfate hemihydrite or anhydrite) with the water to form hydrated gypsum (calcium sulfate dihydrate). Prior apparatus and methods for addressing some of the operational problems associated with the production of mixed gypsum are disclosed in commonly-assigned U.S. Pat. Nos. 6,494,609 and 7,007,914; both of which are incorporated by reference in their entireties. A gypsum wallboard mixer typically includes a housing defining a mixing chamber with inlets for receiving calcined gypsum and water, among other additives well known in the art. The mixer includes an impeller or other type of agitator for agitating the contents to be mixed into a mixture or slurry. Such mixers typically have a circular, tangential discharge gate or slot with a cutoff block or door. The discharge gate controls the flow of slurry from the mixer, but is difficult to adjust or change the slurry flow when product requirements change, such as when thicker or thinner wallboard is desired.
Conventionally, the tangential discharge gate or slot is disposed at an outlet of the mixer in a peripheral wall for the discharge of the major portion of the slurry. A flexible hose having a generally circular cross-section is inserted into the generally rectangular discharge gate for transporting slurry to a desired location, such as the moving conveyor belt of a wallboard production line. However, due to the disparity of the respective cross-sectional geometries of the discharge gate opening and the hose, the hose does not capture the entire potential slurry flow volume from the gate, especially that portion of the slurry circulating above the top of the circular gate opening. As a result, some portions of the slurry in the mixer or the discharge gate keep flowing in the mixer and re-entering into the mixing chamber. In some cases, the slurry has been known to prematurely preset inside the mixer or the discharge gate, which is undesirable due to the production of lumps in the resulting wallboard, and increased labor needed for cleaning the mixer chamber of preset particles.
In conventional mixers, the slurry portions traveling at the highest and/or lowest points of a circular inlet/outlet opening of the discharge gate fail to escape completely from the mixer, and continue to circulate in the mixer, thereby creating slurry lumps and thickening slurry chunks. As a result, in some applications, the circular discharge gate causes slurry flow problems, such as premature setting, buildup, and clogging, and thus makes it difficult to efficiently deliver the mixed slurry through from the mixer to the outlet opening of the discharge gate.
Therefore, there is a need for an improved discharge gate that provides a consistent, even flow of the gypsum slurry from the mixer to the outlet opening of the discharge gate for promoting a smooth delivery of the mixed slurry during operation.